Measuring blood flow in organs is useful in a variety of diagnostic and therapeutic procedures. Magnetic resonance imaging (MRI) can be used for such measurements. In some cases, blood flow is measured using MRI based methods that use exogenous contrast agents such as gadolinium to track blood through an organ, which can have certain risks. Some MR methods label the inflowing blood using magnetic resonance techniques (e.g., saturation or inversion of carotid blood) using special radio frequency (RF) coils or pulse sequences. Such methods suffer from low sensitivity, low resolution, and a limitation on the duration of time that blood can be tracked due to loss of coherence of tagged blood.